Method and apparatus for web forming

Abstract

A method and apparatus for forming a web wherein a fiber suspension from a head box is fed on a section of a forming wire formed by a first, substantially horizontal dewatering zone, and where the web being formed is thereafter led to a second dewatering zone where an upper wire is caused to cover said web, and both wires together with the web between them are led over a turning member. In the twin wire dewatering zone the wires bend upwards. After the turning member the web runs further linearly between the wires obliquely upwards. The web and the lower wire run around a pick-up suction roll and the upper wire leaves the web. The dewatering in the dewatering zones occurs only in one direction, i.e. through the forming wire.

We claim: 
     
       1. A web forming method which consists of feeding a fiber suspension from a head box on a section of a lower forming wire comprising a first, substantially horizontal dewatering zone, covering the web with an upper wire, leading the lower wire and the upper wire with the web therebetween to a second dewatering zone, which is a twin dewatering zone upwardly over a deflecting member having a large radius of curvature, said deflecting member being impervious to water, removing the water from the web in the first and second dewatering zone through only said lower wire, deflecting the web in a substantially straight path upwardly in a direction which deviates from the horizontal original direction of travel of the web, by an angle less than 90° up to a suction roll, said deflecting member being located in the upper wire, then detaching the upper wire from the web, causing said upper wire to continue to travel beyond the suction roll upwardly in essentially the same direction as it was upstream of said suction roll, and removing the web from the lower wire. 
     
     
       2. A web forming method according to claim 1, wherein 50 to 90% of the water flowing from the head box is removed in the first dewatering zone. 
     
     
       3. An apparatus for forming a web from a fiber suspension comprising a lower wire loop, a head box for feeding the fiber suspension onto said lower wire loop, at least one dewatering member having a curved impervious surface with a large radius of curvature inside the loop, said wire loop having a first horizontal section, an upper wire disposed to cover the web located over the lower wire, guide rolls being located inside the upper wire, means for moving said upper and lower wires with the web therebetween to a deflecting member, said deflecting member being impervious to water and having a large radius of curvature, and being located in the upper wire, wherein the direction of travel of the web and the wires is deflected upwards by an angle smaller than 90° to travel upwardly in a substantially straight path, a suction roll arranged within the lower wire, means for detaching the upper wire from the web downstream of the suction roll, said guide rolls leading said upper wire upwardly essentially in the same direction as it was upstream of the suction roll, the radius of curvature of said deflecting member being equal to or greater than the radius of curvature of said guide rolls, and means for detaching the web from the lower wire. 
     
     
       4. A web forming apparatus according to claim 3 wherein the curved surface impervious to water is formed by a rotating roll. 
     
     
       5. A web forming apparatus according to claim 3 wherein inside the upper wire loop there is a rotating roll.